Mating pattern in natural populations of Pseudotsuga menziesii (Mirb.) Franco in Mexico

The Mexican populations of Pseudostuga menziesii (Mirb.) Franco have a restricted and fragmented natural distribution, especially in the central region, therefore there is a risk that these populations will be lost due to the effects of climatic change. With the purpose of suggesting adequate measures for their conservation, an evaluation was made of the mating pattern and its effect on the inbreeding level in three natural populations of P. menziesii, two of the north and one of the central region of Mexico, based on the percentage of cross pollination. With the information of five polymorphic loci, the allelic frequencies of pollen and ovules were estimated, along with the proportion of mating in each population using multilocus ((t) over cap (m)) and single locus ((t) over cap (s)) models. No differences were found in the allelic frequencies of pollen and ovules, which indicates that the pollen comes from the same community as the mother trees. The value of (t) over cap (m) in the two northern populations was close to 90%; in the central population it was 49% as a result of a high percentage of selfing. The similarity of the estimations of the degree of cross breeding ((t) over cap (m) and (t) over cap (s)), indicates that selfing is the principal form of inbreeding in the populations evaluated. Despite the high percentage of cross breeding in the northern populations, the paternity correlation coefficient in them was over 60%, indicating a reduced number of pollinating trees. The implications of these results in the conservation of the populations are discussed, especially in the central region.